IET Science, Measurement & Technology
ISSN / EISSN : 1751-8822 / 1751-8830
Current Publisher: Institution of Engineering and Technology (IET) (10.1049)
Total articles ≅ 1,341
Latest articles in this journal
Published: 15 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12070
Considering that the working temperature is much higher in high‐voltage direct‐current (HVDC) convert transformers than in conventional AC transformers, the combination of thermally upgraded paper and natural ester might be a better choice to withstand high temperature in long‐term operation. This study compares the chemical structure, DC breakdown voltage, space charge and trap distribution of thermally upgraded paper aged in natural esters and mineral oil. The relationship between DC breakdown and accumulated charges was analyzed. Results show that the thermally upgraded paper aged in natural ester (NEI‐TUP) has a higher volume resistivity and DC breakdown voltage than that aged in mineral oil (MOI‐TUP). The NEI‐TUP group has a larger deep trap density than the MOI‐TUP group due to the chemical structure of natural ester. The larger deep trap density could contribute to the lower charge accumulation quantity and higher DC breakdown voltage. The thermally upgraded paper immersed in natural ester presents better insulation capability under thermal and DC electrical stress than that immersed in conventional mineral oil. This research indicated that the combination of thermally upgraded paper and natural ester might be a potential alternative for the mineral oil immersed paper in the future.
Published: 14 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12067
A reliability‐based optimal μ‐PMU (micro‐phasor measurement unit) placement scheme is suggested for efficient observability enhancement of smart distribution grids at steady‐state and contingencies conditions. This article introduces a unique method for the μ‐PMU allocation in reconfigurable smart distribution grids in which communication system requirements and zero injection nodes (ZINs) are considered. The original objective function and limitations are proposed aiming at minimizing the capital cost, including communication links and installation costs of μ‐PMU, optical power ground wire cost, power losses cost, and reliability cost as well as obtaining the maximum number of measurement redundancy constrained to full system observability in the presence of ZINs and tie switches. The suggested method is formulated as a mixed‐integer linear programming problem applied to find optimal μ‐PMU locations considering the cost of communication infrastructure and co‐optimize the system switching plan simultaneously. In this regard, CPLEX—a high‐performance mathematical solver—is used to solve the proposed mixed‐integer linear optimization problem to reach the global optimality. The simulations are performed on 33, 69, and 85‐bus radial distribution networks, and comprehensive simulation studies show the effectiveness of the suggested method.
Published: 8 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12068
In this paper, neural network‐based data fusion is used to detect fault and isolate stator winding short circuit, outer bearing race, and broken rotor bar defects in an induction motor. In addition, the robustness of the proposed method against the disturbance introduced by the coupled pump's unbalanced power source and dry running is investigated. First, three‐phase current and voltage signals are separated by means of independent component analysis (ICA), then extracted features are combined by adopting neural networks, and finally, the system's health condition is evaluated. Experimental results indicate that data fusion based on neural networks can evaluate with high reliability the system's health condition and provide better robustness in the presence of disturbances.
Published: 7 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12064
The impulse impedance of the tower is the core parameter to evaluate the lightning protection performance of the transmission line. The high soil resistivity and the underground rock layers in the mountainous areas will induce large impulse impedance and further lead to frequent lightning striking accidents. Therefore, this paper proposes a circuit‐finite element model (CFEM) and investigates the corresponding impedance‐reduction optimization method of the grounding device in mountainous areas. The model takes into account the nonlinear characteristics of the soil. Based on the parallel‐plate electrode and the concentric hemispheric test device, the nonlinear curves of the soil resistivity of five typical kinds of soils with the electric field intensity are obtained. To justify the CFEM, the field experiment of a single horizontal conductor is performed, with an average relative error of 4.67%. Based on the CFEM, this paper presents an impedance‐reduction optimization method for the grounding device in the mountainous areas, while proposing the best design method and the optimal layout of the grounding device in the rocky zone. The research results can provide a reference for the design transformation and protection optimization of the transmission tower grounding device in mountainous areas.
Published: 7 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12065
The modelling of twisted pair copper cables has been under investigation in recent years with the emergence of several forms of digital subscriber line broadband access technology including G.fast. Designers of these communication systems implement these models to prototype early system architectures as well as simulate feasibility trials on the existing subscriber loop infrastructure. Previous attempts at modelling these cables have been limited because of the challenges associated with acquiring physical measurement and the inaccuracies of simulators to model effects such as the skin effect, which is significant when using these cables in high‐speed systems. These previous modelling attempts employed empirical formulas to match the measured primary transmission line parameters (RLCG) of the cables and generally failed to meet the Kramer–Kronig causality relationships. This paper presents a measurement setup for the electrical properties of twisted pair copper cables as well as a realizable RLCG model for the cables. This model is based on electromagnetic theory considering the model causality, the skin effect, and the twisting of the cable.
Published: 7 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12071
Planar inductive sensors are widely used for non‐contact gap measurement. Usually, a change in size, shape, or material of the target requires a tedious recalibration of the measurement setup. This paper aims to present a new method to measure the gap from irregular and narrow targets using a planar inductive sensor without this tedious calibration process. The magnetic field distribution on this target was numerically studied, and the findings suggested that a simpler calibration would work by modeling the induced current in the target as a virtual planar coil. For this target, we found that the calibration curves corresponding to different materials can be obtained by adding a constant C to the base curve. To validate this approach, three planar coils of different sizes were tested with four metallic turbine blade‐shaped targets. Results showed that the measured gaps matched well with the real gaps, with a maximum error of about 3.703%. The new approach can be applied to various applications including 3D printer build platform calibration, bandsaw blade deviation detection, and blade tip clearance monitoring.
Published: 7 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12066
This paper utilizes a hybrid Debye model to accurately simulate the relaxation response process of the oil‐paper insulation of a transformer to explore the application of frequency domain dielectric spectroscopy (FDS) in nondestructive diagnosis of the aging condition of oil‐paper insulation. Via FDS test data, the model parameters can be identified, and the influence laws of FDS can be obtained through the variation of model parameters. To explore the effects of insulating paper moisture content, insulating paper layers, and test temperature on FDS characteristics, an FDS experimental platform is established. The results show that the hybrid Debye model can effectively reflect the relaxation response process of oil‐paper insulation under different conditions, as well as that a physical relationship between the model parameters and oil‐paper dielectric polarization exists. In addition, the parameters of the hybrid Debye model can be used as the characteristic quantities for the non‐destructive evaluation of the oil‐paper insulation state, providing new ideas for the non‐destructive evaluation of the oil‐paper insulation state.
Published: 3 May 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12069
This paper reports on the influence of thermally induced self‐assembly shish‐kebab crystal on charge transport behaviour in polypropylene (PP) and PP/propylene‐based elastomer (PBE) blends. The film samples with the shish‐kebab crystal were prepared by adding a β nucleating agent TMB‐5 under thermally induced self‐assembly. Polarised optical microscope （POM）, X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements were performed to understand the crystallisation characteristics of samples. Carrier trap distribution was analysed by isothermal surface potential decay (ISPD) method, and DC breakdown strength measured as well. The decrease of shish‐kebab crystal size, the reduction of trap level, the increase of shallow trap density and the decrease of deep trap density were obtained with the TMB‐5 content. The hopping distance of charges decreased with the shallow trap density increasing. The DC breakdown strength for PP/PBE/TMB‐5 was higher than that for PP/TMB‐5. It is suggested that deep traps are formed on the clear shish‐kebab crystal boundaries, while shallow traps are induced by the elastomer and the un‐crystallisation nucleating agents. Both the carrier trap formation on the crystal boundary and the physical channel orientation of the shish‐kebab crystals affect the charge transport behaviour.
Published: 26 April 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12063
It is often more complicated to measure the phase response of a large system than the magnitude. In that case, one can attempt to use the Kramers–Kronig (KK) relations for magnitude and phase, which relates magnitude and phase analytically. The advantage is that then only the magnitude of the frequency response needs to be measured. It is shown that the KK relations for magnitude and phase may yield invalid results when the transfer function has zeros located in the right half of the complex s‐plane, that is, the system is non‐minimum phase. In this paper, a method which enables to determine these zeros is proposed, by using specific excitation signals and measuring the resulting time responses of the system. The method is verified using blind tests among the authors. When the locations of the zeros in the right half of the complex s‐plane are known, modified KK relations can be successfully applied to non‐minimum phase systems. This is demonstrated by computing the phase response of the electric field, excited by a point dipole source inside a closed cavity with Perfect Electrically Conducting (PEC) walls. Also, the effects of simulated measurement noise are considered for this example.
Published: 23 April 2021
IET Science, Measurement & Technology; doi:10.1049/smt2.12062
In order to effectively detect the internal insulation defects of large transformers, a miniature patrol robot fish is designed and used to observe the pressboard inside the transformer, which can visually inspect the insulation condition of the pressboard. In the process of visual inspection by a patrol robot fish, insulation defects observed in the transformer (such as discharge carbon marks, pressboard cracks, etc.) are small size, indistinctive colour contrast and different shapes. The key purpose of the patrol robot fish is to identify the defect targets and defect types intelligently and quickly from the images taken by the camera on the fish. Considering that there are abundant insulation defects in transformers and a lack of samples for learning, a vision detection method based on deep learning network is proposed in this study. The proposed method integrates the variable autoencoder into the traditional Faster‐RCNN target detection network and constructs an improved Faster‐RCNN that enhances feature extraction. This method expands the small‐scale training sample set and improves the generalisation performance of the model. In order to verify the effectiveness of the proposed method, the improved network is trained and tested, and the test results show that the improved network training model can accurately identify and mark the carbon marks on the pressboard surface.